This invention arises out of the electronic industry, and more specifically out of the industry that has built up for manufacture of printed circuit boards, printed circuit film, and the treatment of like articles. In this industry, and related fields, such as the electroplating industry, it has become commonplace that where an article is to be treated, if there are portions of the article that are not to be treated, such as by etching, plating, or the like, a barrier will be provided to those portions that are not to be treated, in the form of a coating of material which is later to be removed. Typically, where plating or etching are the treatments involved, the coating will be in the form of a mask that is applied to the printed circuit board or other article, which mask prevents the treatment fluid, generally liquid, from having any chemical effect such as etching or plating on the article in those locations where the mask is applied. This is because the mask is generally selectively applied to only those portions of the article that are not to be treated. After the etching, plating, or the like is accomplished, the mask is then chemically treated by applying a solution to it that chemically removes it from the article. Typically, such a solution is an acidic or alkaline solution that breaks down and separtes the mask from the article, often while it is being conveyed through a solution-spraying chamber.
In the past, many such chemical solutions that remove the masks, coatings, or the like, have been chemically structured to dissolve the mask in the solution. When this has been the case, the material of the mask can build up in the solution until it reaches an unacceptably high concentration, in which case the solution can either be discarded or subjected to a subsequent reclamation operation. In the past, many such masks have been of a water-soluble type that have lent themselves to being discarded into sewage systems, along the with solutions.
Increased environmental concern has lead to the development of other masks or coatings, including some that are not water-soluble, such as polymers and the like, including masks that are also not soluble in the solutions that are used to remove them from the underlying articles such as printed circuit boards or the like. Thus, while the chemistries that are used to separate the polymers or other masks from boards or other articles are able to quickly remove the masks from the articles, they leave the removed material often in a range of physical states ranging from a gelatinous consistency, to particles such as relatively inert flakes or skins, which may remain in the solution almost indefinitely without dissolving.
With the increased development of the electronic industry, an ever-increasing demand has been placed on the development of article treatment apparatus that is capable of highspeed automatic processing, particularly for printed circuit boards and the like. This necessarily produces a demand for high processing rates for the management of skins and debris that result from removing etching and plating resists or masks from panels. This necessarily results in demand for higher processing rates with respect for removal of accumulated residue from the solutions that have been used to remove the masks from articles.
In the past, in most filtration situations, the filtrate or filter cake is permeable, which enables the filter action to continue, until the aggregate accumulation of the filtrate slows down the liquid passage to an inefficient level. For example, in U.S. Pat. No. 3,776,800, a removable filter is taught, as is used for removing particles from an etching solution. Also, the removable of resists and other masks from articles being treated is taught in U.S. Pat. No. 4,015,706, as some of the treatment functions to which the present invention is addressed.
In the case of some masks or resists, particularly when they are polymers, the presence of the skins, flakes, etc., which comprise the polymer or other mask, because of their ability to attach themselves to the screen or other filter, may render the screen or other filter inoperable, by sealing or clogging the screen or other filter.